Points of Refrigerant Control of VRV System
Si30-408
26
Basic Information
3.3
Compressor Capacity Control
In the compressor capacity controller of VRV system, the pressure detected (Pe or Pc) by
pressure sensor installed in outdoor unit is converted into equivalent saturation temperature,
and the evaporation temperature (Te) while cooling or the condensation temperature (Tc) while
heating are so controlled with PI control as to put them close to the target value in order to
maintain stable capacity in spite of incessantly varying load. (Refer target value below table.)
*Above all target temperatures mean saturation temperatures on gas sides.
The pressure loss in piping increases depending on connecting piping length and operation
capacity of compressor. In order to compensate capacity lowering caused by the pressure loss
in piping, the following correction are made.
Correction of Target Evaporation Temperature by
∆
P.
Target value adjustment can be made through field setting.
Long connection piping at the installation site may increase pressure loss in piping and an
inverse installation (outdoor unit is placed lower than indoor unit) may increase liquid pipe
inside resistance. In such case, "lower" setting of target evaporation temperature by using
field setting will give stable operation.
On the other hand for short connection piping, higher setting will make stable operation
easy.
In addition, samplings of evaporation temperature and condensation temperature are so made
that pressure detected by every pressure sensors of high/low pressure are read every 20
seconds and calculated. And every time the compressor capacity (INV frequency or STD ON/
OFF) is controlled to eliminate deviation from target value.
P(MPa)
Target condensing temperature
Target evaporating temperature
Discharge pressure Pc :
Detected by high-pressure sensor
Suction pressure Pe :
detected by low-pressure sensor
h (KJ . kg
-1
)
∆
P = pressure loss
(caused by compressor operation capacity and
piping length)
Target condensation temperature /
High pressure
Target evaporation temperature /
Low pressure
R22
46°C
1.8MPa
5.5°C
0.59MPa
R407C
48°C
1.9MPa
7.5°C
0.58MPa
R410A
46°C
2.8MPa
6.0°C
0.96MPa
Target evaporation temperature
Target evaporation
temperature setting
Compressor operation capacity
: "Higher" setting
: "Normal" setting
(factory setting)
: "Lower" setting
Max
Min
+3Cº
–3Cº
